Whole Kidney Volume/Pressure Relationships and Renal Function: Marked renal swelling is commonly seen in states of acute renal injury such as ischemic acute renal failure or transplant rejection. We have shown that acute expansion of renal parenchymal volume above normal impairs renal function. The mechanism is unknown. However, using renal arterial injection of Microfil, we have found striking evidence of stretching of afferent arterioles in swollen rejecting canine allografts, but not in normal dog kidneys. We have also recently provided indirect evidence that marked renal parenchymal expansion is principally the result of a marked decrease in tissue cohesive forces. Presently, little is known about the perturbations in tissue forces which cause renal swelling or the means to regulate these forces. We intend to identify the nature of the perturbation of tissue cohesive forces, solid tissue forces and interstitial fluid forces which cause renal swelling and, guided by outcomes of these studies, search for means by which control of swelling can be achieved to favorably affect renal function. Factors Regulating the Tissue Uptake of Circulating Immune Complexes: Our second major investigative theme has as its principal feature new methodologies for examining the avidity with which tissues trap circulating immune complexes: we have reported techniques to assess the absolute and fractional uptake of circulating immune complexes by the major organ systems, including specifically the glomerular capillary bed. We are using this approach to examine the hemodynamic, pharmacologic, and biochemical determinants of immune complex trapping. In addition, these methodologies and certain of the techniques used to examine the mechanism of tissue swelling will be used to define the relationship between capillary ultrafiltration and the uptake of circulating immune complexes. This is thought to be a key relationship, however, its role in immune complex trapping has not been critically examined.